Various embodiments relate to molecular sieve blends containing a combination of a hydrophilic zeolite, and a hydrophobic silicon based binder and preferably, a seed, preferably formed in a granulation process, utilized in the preparation of the molecular sieve blends, wherein the seed, in one embodiment, contains a clay binding agent, and processes of manufacture and use of these molecular sieve blends, such as for dehydration of liquid and gaseous hydrocarbon streams, drying of cracked C1-C4 hydrocarbon gas streams, dehydration of ethanol feed streams, and removal of various undesired materials from various types of feed streams. (For purpose of this disclosure “molecular sieve blends” are alternatively referred to as “adsorbents”, “adsorbent blends”, “molecular sieve adsorbent blends” or “molecular sieve adsorbents” or similar terms.)
Zeolites are hydrated metal alumino silicates having the general formulaM2/nO:Al2O3:xSiO2:yH2Owhere M usually represents a metal of an alkali or alkaline earth group, n is the valence of the metal M, x varies from 2 to infinity, depending on the zeolite structural type and y designates the hydrated status of the zeolite. Most zeolites are three-dimensional crystals with a crystal size in the range of 0.1 to 30 μm. Heating these zeolites to high temperatures results in the loss of the water of hydration, leaving a crystalline structure with channels of molecular dimensions, offering a high surface area for the adsorption of inorganic or organic molecules. Adsorption of these molecules is dependent upon the size of the zeolite channels. The rate of adsorption is limited by the laws of diffusion.
Zeolites are used for a number of processes. The choice of zeolite is important in a number of chemical processes well known to those skilled in the art. For example, catalytic processes of interest using zeolites in the petrochemical industry include reforming, hydrocracking, dewaxing, isomerization, fluid catalitic cracking (FCC), partial oxidation, alkylation and disproportionation of aromatics. Zeolites are also used for dehydration, adsorption of various compounds from feed streams and separation of various hydrocarbons in a feed stream.
Molecular sieves have been advantageous for a number of processes as the diffusion of materials into and out of the pores can be facilitated based on the pore size that is present within the particular molecular sieve. (For purposes of this disclosure “zeolite” and “molecular sieve” have the same meaning.)
One limitation on the utilization of zeolites is their extremely fine particle size. Large, naturally-formed agglomerates of zeolite crystals break apart easily. In addition, because the pressure drop through a bed containing only such fine zeolite crystals is prohibitively high, these zeolite crystals cannot be used alone in fixed beds for various dynamic applications, such as drying of natural gas, drying of air, separation of impurities from a gas stream, separation of some gaseous and liquid product streams and the like. Therefore, it is necessary to agglomerate these zeolite crystals with binder materials to provide an agglomerate mass containing the zeolite crystals, which exhibits a reduced pressure drop.
To overcome these issues and permit the utilization of zeolite crystals, different types of clays have conventionally been used as binder materials for those crystals, wherein the clay binders have generally been selected from attapulgite, palygorskite, kaolin, sepiolite, bentonite, montmorillonite, other types of clays and mixtures thereof. Particularly useful clay binders are formed from attapulgites.
In one example of the utilization of a molecular sieve adsorbent, water is removed from a cracked gas stream, for example, for the production of ethylene. The molecular sieve adsorbent is utilized immediately before a cryogenic process to remove water so that ice is not created during the process. However, inherent in the process is the fact that the hydrocarbon feed stream contains unsaturated hydrocarbons, such as alkenes and dienes, which are very reactive. These unsaturated hydrocarbons tend to form oligomers and polymers, which act as bed fouling agents and are commonly referred to as green oil or coke. These agents block adsorption channels, reduce the working capacity of the bed for dehydration and reduce useful adsorption life of the adsorbent. Accordingly, it is also important that the molecular sieve adsorbents produce very low quantities of green oil or coke during an adsorption process. Many of the clay binders that have been traditionally used as binder materials with zeolites contain metallic acid sites that encourage polymer/oligomer formation by a catalytic reaction. Conventionally, these clay binder materials are treated with a de-activating agent such as a phosphate solution to reduce this catalytic activity. Notwithstanding, there are still issues associated with the production of green oil/coke during processes for treatment of hydrocarbon feed streams when clay materials are used as the binder material with zeolites.
Silicon based materials have sometimes been used as a binder material with high silica molecular sieves to form catalyst agglomerates for specialty catalytic reactions, wherein the molecular sieves used have included, for example, ZSM-5, Y zeolites and SAPO zeolites. Because of the hydrophobic nature of both the silicon based binders and the high silica zeolites, these catalytic materials have been limited in use to organic reactions. For example, hydrophobic silicon based binders blended with hydrophobic high silica zeolites have been utilized as catalytic materials in the petrochemical industry for reactions including reforming, hydrocracking, dewaxing, isomerization, partial oxidation, alkylation, disproportionation of aromatics, and particularly as fluid catalytic cracking catalysts. These catalytic reactions conventionally utilize hydrophobic zeolites having a high silica content, wherein the SiO2:Al2O3 ratio is at least 50, preferably greater than 200 and as high as 600 or so. To enhance the high silica content of these zeolites, they are often dealuminized to increase their silica:alumina ratio, making them even more hydrophobic. The silicon based binders used with these catalysts are also required to be highly hydrophobic. Binders used to produce catalysts for these catalytic reactions are not included within this disclosure. Further, the binders of this disclosure are not conventionally utilized to form these catalysts.
One problem with many conventionally formed zeolite agglomerate blends is decreased diffusion. The larger the diameter of the formed zeolites, the slower the rate of diffusion of the molecules to be adsorbed. Particularly in the field of pressure swing adsorption, this effect is highly adverse to short cycle time and thus to productivity. Enhanced kinetic values or faster mass transfer rates can result in shorter cycle time and lower power consumption and thus higher adsorbent productivity.
Another important issue in choosing an appropriate adsorbent is the ability of that adsorbent to selectively adsorb a compound that is desired to be removed from the processing stream without also adsorbing the desired component or components of that stream. For example, an important feature of adsorbents used to remove water from an ethanol feed stream is not only their water adsorption capacity but also that the quantity of ethanol that is adsorbed by the adsorbents is limited. Frequently, it is necessary to balance the relative adsorption capabilities of these adsorbents.
Accordingly, it is one intent to disclose a process for the production of molecular sieve blends which are effective and highly selective for the removal of water from hydrocarbon feed streams, such as those containing ethanol or cracked gases.
It is a still further intent to disclose molecular sieve blends which maintain their physical properties and diffusion capabilities even with a reduced quantity of binder than is conventionally used.
It is a still further intent to disclose molecular sieve blends which limit the production of undesired oligomers and polymers during utilization.
It is an additional intent to disclose a process for the preparation of molecular sieve blends with enhanced diffusion rates.
It is a still further intent to disclose a process for the production of molecular sieve blends containing a hydrophobic silicon based binder that are effective and selective for adsorption processes.
It is a still further intent to disclose molecular sieve blends comprising a low silica, hydrophilic zeolite blended with a hydrophobic silicon based binder.
It is a still further intent to disclose molecular sieve blends comprising a low silica, hydrophilic zeolite, a hydrophobic silicon based binder and a seed comprising, in one embodiment, a clay binding agent, wherein a granulation seed process is utilized to produce the seeds used for the production of the molecular sieve blends.
It is a still further intent to disclose molecular sieve blends comprising a low silica, hydrophilic zeolite blended with a hydrophobic silicon based binder, and a seed, preferably comprising a clay binding agent, wherein a granulation seed process is utilized for the production of the seed, and wherein the seeds utilized in the granulation seed process comprises less than 25% by volume of the molecular sieve blends.
It is still further intent to disclose molecular sieve blends comprising a low silica, hydrophilic zeolite blended with a hydrophobic silicon based binder and a seed, preferably comprising a clay binding agent, wherein a granulation seed process is utilized for the production of the seed, wherein the composition of the seeds comprises clay and the hydrophilic zeolite, and wherein the clay comprises less than 5% by weight of the overall molecular sieve blends.
It is a still further intent to disclose a process for drying a feed stream comprising passing the feed stream over molecular sieve adsorbent blends comprising a low silica, hydrophilic zeolite, a hydrophobic silicon based binder, and a seed used for the production of the molecular sieve blends, preferably comprising a clay binding agent and the hydrophilic zeolite.
It is a still further intent to disclose a process for the separation of polar materials using molecular sieve blends comprising a zeolite, particularly a low silica hydrophilic zeolite, more particularly a low silica hydrophilic zeolite 3A, a hydrophobic silicon based binder, particularly a hydrophobic colloidal silica binder or, in a less preferred embodiment, a hydrophobic siloxane based binder, and a seed used in the production of the molecular sieve blends, preferably comprising a clay binding agent and the hydrophilic zeolite.
It is still further intent to disclose a process for separation of components of a gaseous or liquid feed stream, particularly an ethanol feed stream, comprising passing that gaseous or liquid feed stream over molecular sieve blends comprising a low silica hydrophilic 3A zeolite powder, a hydrophobic colloidal silica binder or, in a less preferred embodiment, a hydrophobic siloxane based binder, and a seed used in the production of the molecular sieve blends, preferably comprising a clay binding agent and the hydrophilic zeolite.
These and other intents are obtained from the processes for production, the processes for use and the products of the various embodiments disclosed herein.